Delivery of therapeutic proteins may now be feasible by using implants of genetically modified endothelial cells. These cells may be the ideal vehicles for drug delivery because of their direct contact with the bloodstream. Moreover, in the context of the large surface area afforded by a microvascular capillary network, large numbers of endothelial cells would be available to deliver recombinant gene products for either local or systemic actions. The components of such a genetically-modified cellular drug delivery system now exist: (a) the genes for therapeutically useful proteins such as growth hormone have been cloned; (b) retroviral vectors can efficiently introduce functional genes into endothelial cells; (c) established methods now exist for the isolation and cultivation of these cells; and (d) vascularization of cell-containing biomatrix implants can be elicited by the application of an angiogenesis factor. Our goal is to exploit the availability of high efficiency retroviral- mediated gene transfer and the potent angiogenic activity of acidic fibroblast growth factor (aFGF) in order to test the hypothesis that genetically modified endothelial cells can be stably incorporated into neovessels induced by an angiogenesis factor. We propose to culture microvascular endothelial cells (RMEC) from inbred rats and to transduce them with retroviral vectors containing the E. coli lacZ gene. We will use the lacZ gene product, beta-galactosidase, to select for lacZ-expressing cells with flow cytometry and to visually track those cells in vivo with X-gal staining. The lacZ-expressing RMEC will be immobilized within an aFGF-containing biomatrix and implanted in animals. The fate of the implanted cells will be studied with X-gal histochemistry. As an extension of these studies, RMEC will be transduced with the rat growth hormone gene (rGH) and implanted in dw/dw growth hormone deficient rats. These studies should advance our understanding of the molecular and biological components of a therapeutic drug delivery system that utilizes genetically-engineered endothelial cells.